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r 23 May 2003 AGE-NC Project No 95-0184 ' Page 7 of 9 prevalent and coarser (gravelly sand Identified at 95 feet) with depth Based on ' CPT-generated lithologic properties, AGE Identified a vadose zone extending from surface grade to approximately 35 feet bsg and fourteen hydrologic units Five hydrologic units ' (HU5, HU7 and HU9, HU11 and HU13) are sand-bearing units of low dynamic pore pressures,the remaining units are predominantly zones of inter-bedded clayey silt,silty clay, clay and stiff fine-grained sediment, with occasional, laterally discontinuous sand lenses, ' pore pressures within these intervals vary from low to high • The most recent ground water monitoring data place depth to ground water at approximately 35 feet bsg, however, historical ground water data compiled by the San Joaquin County ' Flood Control and Water Conservation District between 1970 and 2003 indicated that ground water at the site has been as deep as 70 to 75 feet bsg The dominant ground water flow ' direction is generally northward across much of the site,however,in the southeastern portion of the site the inferred ground water flow direction is generally easterly 4bi.,S e -r`.' • On 24 April 1987, one 1,000-gallon gasoline underground storage tank (Tank A) was _ I ' remo d from the northwestern corner of the site,on 19 October 1988,one 300-gallon waste oil UST(T B)was removed from the site near the northern property line and the canopy, 4\ , and on 25 May 1990, one 1,000-gallon gasoline UST and one 1,000-gallon diesel UST ' (Tanks C & D) were removed from beneath the sidewalk at the southeastern corner of the 12, site Petroleum hydrocarbons were detected in soil samples collected beneath tanks A,C and D, only low concentrations of TCE and chloroform were detected in the sample collected ' beneath Tank B • The timings of the releases from the USTs are unknown, however, once released to the ' subsurface, the contaminants migrated vertically and laterally The deep vertical extent of contaminated soil and ground water at the site suggests that the releases occurred when ground water elevation was low, either during a drought penod(s) and/or a period of heavy ' ground water withdrawal • The cores of highest contaminated soil appear to be from between 35 and 45 feet bsg at the ' northern tank location and at approximately 25 feet bsg at the southern tanks location, however, the lateral and vertical extent of contaminated soil has not been defined at either - G locations • Petroleum hydrocarbon compounds and VOCs have been detected in ground water to the total depth of the CPT borings (approximately 180 feet bsg), the highest,concentrations of ' contaminants in water samples collected from the CPT borings were generally from hydrologic units in fine-grained soil Laterally,the extent of ground water contamination has not been defined I IAdvanced GeoEnviron mental,Inc I